Keep horizontally scrolled content out of the inclusion gutter

If a view that shows the inclusion gutter is scrolled horizontally, its
content is drawn over the gutter. The marker of a marked line is
overwritten, and the content starts the gutter's width too far to the
left. The draw loop skips the cells scrolled past the left edge only
until x reaches 0, but the content area starts at the gutter's width.

Nothing scrolls such a view horizontally yet. A later commit lets the
focused main view scroll sideways, and the gutter shows there while
building a custom patch.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

pkg/gocui/view.go

@@ -1878,7 +1878,7 @@ func (v *View) draw(isWindowFocused bool) {
 
 		var c cell
 		for x < maxX {
-			if x < 0 && cellIdx >= len(vline.line) {
+			if x < gutterWidth && cellIdx >= len(vline.line) {
 				// no more characters to write so we're only going to be printing empty cells
 				// past this point
 				x = gutterWidth
@@ -1891,8 +1891,9 @@ func (v *View) draw(isWindowFocused bool) {
 				c = vline.line[cellIdx]
 			}
 
-			// Skip the cells scrolled out to the left.
-			if x < 0 && x+c.width <= 0 {
+			// Skip the cells scrolled past the left edge of the content area; the
+			// content area starts after the gutter.
+			if x < gutterWidth && x+c.width <= gutterWidth {
 				x += c.width
 				cellIdx++
 				continue
@@ -1901,10 +1902,10 @@ func (v *View) draw(isWindowFocused bool) {
 			// A terminal can't show half of a double-width character, so one that is cut
 			// off by the left or right edge shows as a blank in the column of it that is
 			// on screen.
-			if x < 0 || x+c.width > maxX {
+			if x < gutterWidth || x+c.width > maxX {
 				c.chr = " "
 				c.width = 1
-				x = max(x, 0)
+				x = max(x, gutterWidth)
 			}
 
 			fgColor := c.fgColor

pkg/gocui/view_test.go

@@ -1326,6 +1326,31 @@ func TestClickHyperlinkBesideTheInclusionGutter(t *testing.T) {
 		opened)
 }
 
+// Content scrolled to the right goes under the gutter, not over it: the gutter
+// stays where it is, and the content shows from the scroll position onwards.
+func TestInclusionGutterWithHorizontallyScrolledContent(t *testing.T) {
+	WithSimulationScreen(t, 14, 6)
+
+	v := NewView("name", 0, 0, 11, 5, OutputNormal) // InnerWidth 10
+	v.InclusionGutterMarker = "✓"
+
+	v.writeString("0123456789abcdef\n0123456789abcdef\n")
+	v.SetInclusionGutter(true, []bool{true, false})
+	v.SetOriginX(3)
+	v.draw(true)
+
+	row := func(y int) string {
+		s := ""
+		for x := 1; x <= 10; x++ {
+			chr, _, _ := Screen.Get(x, y)
+			s += chr
+		}
+		return s
+	}
+	assert.Equal(t, "✓ 3456789a", row(1))
+	assert.Equal(t, "  3456789a", row(2))
+}
+
 // A marked line the view wraps is marked on every segment it is drawn as, so that
 // the mark doesn't look like it belongs to the first part of the line alone. The
 // gutter takes its columns out of the width the content wraps in.